DM(3)

NAME
dm - device-mapper access manipulation library

LIBRARY
libdm

SYNOPSIS
#include <libdm.h>
void
libdm_iter_destroy(libdm_iter_t libdm_iter);
int
libdm_task_run(libdm_task_t *libdm_task);
libdm_task_t
libdm_task_create(const char *command);
void
libdm_task_destroy(libdm_task_t libdm_task);
int
libdm_task_set_name(const char *name, libdm_task_t libdm_task);
char *
libdm_task_get_name(libdm_task_t libdm_task);
int
libdm_task_set_uuid(const char *uuid, libdm_task_t libdm_task);
char *
libdm_task_get_uuid(libdm_task_t libdm_task);
char *
libdm_task_get_command(libdm_task_t libdm_task);
int32_t
libdm_task_get_cmd_version(libdm_task_t libdm_task, uint32_t *ver, size_t size);
int
libdm_task_set_minor(uint32_t minor, libdm_task_t libdm_task);
uint32_t
libdm_task_get_minor(libdm_task_t libdm_task);
int
libdm_task_set_flags(uint32_t flags, libdm_task_t libdm_task);
uint32_t
libdm_task_get_flags(libdm_task_t libdm_task);
uint32_t
libdm_task_get_target_num(libdm_task_t libdm_task);
int32_t
libdm_task_get_open_num(libdm_task_t libdm_task);
uint32_t
libdm_task_get_event_num(libdm_task_t libdm_task);
int
libdm_task_set_cmd(libdm_cmd_t libdm_cmd, libdm_task_t libdm_task);
libdm_cmd_t
libdm_task_get_cmd(libdm_task_t libdm_task);
libdm_cmd_t
libdm_cmd_create(void);
void
libdm_cmd_destroy(libdm_cmd_t libdm_cmd);
libdm_iter_t
libdm_cmd_iter_create(libdm_cmd_t libdm_cmd);
int
libdm_cmd_set_table(libdm_table_t libdm_table, libdm_cmd_t libdm_cmd);
libdm_table_t
libdm_cmd_get_table(libdm_iter_t iter);
libdm_target_t
libdm_cmd_get_target(libdm_iter_t iter);
libdm_dev_t
libdm_cmd_get_dev(libdm_iter_t iter);
uint64_t
libdm_cmd_get_deps(libdm_iter_t libdm_iter);
libdm_table_t
libdm_table_create(void);
void
libdm_table_destroy(libdm_table_t libdm_table);
int
libdm_table_set_start(uint64_t start, libdm_table_t libdm_table);
uint64_t
libdm_table_get_start(libdm_table_t libdm_table);
int
libdm_table_set_length(uint64_t length, libdm_table_t libdm_table);
uint64_t
libdm_table_get_length(libdm_table_t libdm_table);
int
libdm_table_set_target(const char *name, libdm_table_t libdm_table);
char *
libdm_table_get_target(libdm_table_t libdm_table);
int
libdm_table_set_params(const char *params, libdm_table_t libdm_table);
char *
libdm_table_get_params(libdm_table_t libdm_table);
int32_t
libdm_table_get_status(libdm_table_t libdm_table);
void
libdm_target_destroy(libdm_target_t libdm_target);
char *
libdm_target_get_name(libdm_target_t libdm_target);
int32_t
libdm_target_get_version(libdm_target_t libdm_target, uint32_t *ver, size_t size);
void
libdm_dev_destroy(libdm_dev_t libdm_dev);
char *
libdm_dev_get_name(libdm_dev_t libdm_dev);
uint32_t
libdm_dev_get_minor(libdm_dev_t libdm_dev);
int
libdm_dev_set_newname(const char *newname, libdm_cmd_t libdm_cmd);

DESCRIPTION
Every object in libdm has its own create and destroy routine.
•   libdm_task_t
•   libdm_cmd_t
•   libdm_table_t

Except libdm_dev_t which is received from kernel as list of physical devices on which the logical device depends. libdm_target_t which is received from kernel as list of available targets to use. libdm_iter_t which is used as iteration counter for array entries in the task structure.

Every object attribute in libdm can be set and gotten by appropriate routines, therefore there always are set and get routines.

  LIBDM TASK
The libdm_task_create() function creates a libdm task dictionary with command string set to command. If command is NULL, libdm_task_t is not created and the function returns NULL.

libdm_task_destroy() free all memory allocated to libdm_task by libdm_task_create().

libdm_task_run() Sends created libdm_task to kernel and receives new one as reply.

List of attributes avaialable in libdm_task_t:
Attribute | Description | Mode
DM_IOCTL_OPEN | Device open-count | Read-Only
DM_IOCTL_MINOR | Device minor number | Read-Write
DM_IOCTL_NAME | Device name | Read-Write
DM_IOCTL_UUID | Device uuid | Read-Write
DM_IOCTL_TARGET_COUNT | Number of table entries | Read-Only
DM_IOCTL_FLAGS | Device status flags | Read-Write

libdm_task_set_name() and libdm_task_get_name() Set name of the device for commands which need to have a dm device identifier. The device-mapper later uses the device name to look up the device from the list of all devices. The get routine will fetch the device name from the task dictionary.

libdm_task_set_uuid() and libdm_task_get_uuid() Set uuid of device for commands which need to have a dm device identifier. The device-mapper later uses the device uuid to look up the device from the list of all devices. The get routine will fetch the device uuid from the task dictionary.

libdm_task_set_minor() and libdm_task_get_minor() Set minor device number of device for commands which need to have a dm device identifier. The device-mapper later uses the device minor number to look up the device from the list of all devices. The get routine will fetch the device minor number from the task dictionary.

libdm_task_set_flags() and libdm_task_get_flags() Set/fetch device status flags from the task dictionary.

libdm_task_get_open_num() Fetch number of opened devices from the kernel and return them as count.

libdm_task_get_target_num() Fetch number of opened devices from the kernel and return them as count.

libdm_task_get_cmd_version() Get the version of the dm driver in the kernel as array uint32_t *ver of size size. libdm_task_set_cmd() and libdm_task_get_cmd() Add and fetch cmd structure from libdm_task_t. libdm_cmd_t is the container used to carry information specific for the particular command. cmd is usually set before libdm_task_run is used and is taken from the task structure after the task run was called.

  LIBDM TASK CMD
The libdm_cmd_create() function will allocate a cmd structure which can later be put in to the task.

libdm_cmd_destroy() will deallocate a previously allocated cmd structure.

libdm_cmd_set_table() Will load and fetch the device mapping table from the dm device. The table is usually loaded to the device during initial device creation or device resizing.

Because libdm_cmd is an array of structures, all _get routines need an iterator to work. For every entry we can have more than one. libdm_cmd_get_table() When the user creates a task with the "status" command, the kernel sends cmd with a table in it.

libdm_cmd_get_target() Get mapping target description from cmd. Target contains target_name and target_version.

libdm_cmd_get_dev() When user creates a task with the "info" command, the kernel sends cmd with information about dm device to user.

libdm_cmd_get_deps() When user creates a task with the "deps" command, the kernel sends cmd with an array of physical devices attached to the dm device.

Usually the device has more than one table entry in the device command. Therefore cmd iterators are needed for libdm_cmd_t; they can be created by the libdm_cmd_iter_create() function.

  LIBDM CMD TABLE
A device table describes the logical mapping between the dm device and physical devices. Every table has the logical block start, the table length (in disk blocks), the target used by table, the physical device, and the offset on it. The physical device and the offset on it are parameters which are target specific and are passed down to the target as param string.

Example device table entry
    0 1024 linear /dev/wd1a 384
Attribute | Description
DM_TABLE_TYPE | Used device mapper target
DM_TABLE_START | Device Logical start block
DM_TABLE_STAT | Is 1 if this is current active table
DM_TABLE_LENGTH | Logical length described by table
DM_TABLE_PARAMS | Params passed down to target

libdm_table_set_start() and libdm_table_get_start() Set start table from start value to libdm_table argument. Get routine will get the table start from kernel as libdm_table.

libdm_table_set_length() and libdm_table_get_length() Set table length from length value to libdm_table argument. Get routine will get the table length from kernel as libdm_table.

libdm_table_set_target() and libdm_table_get_target() Set target name from target value to libdm_table argument. The target must be actually present in the kernel, otherwise libdm_task_run() will fail. Get routine will get the table entry target from kernel as libdm_table.

libdm_table_set_params() and libdm_table_get_params() Set table target parameter string from params argument to libdm_table. This is later in the kernel passed to the target init routine. Get routine will get the table parameter string from kernel as libdm_table.

libdm_table_get_status() Get table status which can be Active/Inactive. This tells if this table is actually used or not.

  LIBDM_TARGET
libdm_target_destroy() Destroy target received from libdm_cmd with libdm_cmd_iter iterator.

libdm_target_get_name() returns pointer to a string with available target name.

lobdm_target_get_version() Sets argument ver[3] to a in-kernel loaded target version.

  LIBDM_DEV
libdm_dev_destroy() Destroy device received from libdm_cmd with libdm_cmd_iter iterator.

libdm_dev_get_name() Return pointer to a string with underlying device name from libdm_dev_t

libdm_dev_get_minor() Return underlying device minor number.

  MISC
libdm_dev_set_newname() This routine will set new dm device name attribute to newname. User must then called libdm_task_run on this task to change the device name.

RETURN VALUES
Upon success, all described functions return zero or non-NULL pointer. Otherwise, an error number will be returned to indicate the error.

SEE ALSO
dm(4)

HISTORY
The dm was written and contributed to NetBSD by Adam Hamsik and first appeared in NetBSD 6.0.